"mushrat" for "muskrat"?

“Mushrat” (which the n-gram shows from the 1860s onward) is an uncommon regional variation of “muskrat” (which the n-gram has predating “mushrat” by nearly 70 years). I’m wondering if the process whereby “muskrat” begat “mushrat” might be eggcornish. I’m not sure if the perps might have assumed that “mushrats” like to eat mush or that the critters themselves might be mushy or be tasty with mush, or live in mushy, marshy environs. Or maybe they were just more familiar with the word “mush” than “musk”, so misheard/substituted the one for the other. Or maybe they were just mush-mouthed. Anyway, I doubt my confusion about the topic will ever be dispelled. * sigh *